Unlike a primary battery, the secondary battery may be recharged. Lower power batteries are used for various portable electronic devices such as cellular phones, laptop computers, and camcorders. Bulk size batteries are used as the power source for motor drive, such as in hybrid electric vehicles.
Depending on the external shape, secondary batteries may be classified into different types, for example, square and cylindrical batteries. When they are used for motor drive of the machines requiring a high power source such as the hybrid electric vehicles, the secondary batteries (hereinafter “unit battery”) may form a secondary battery module of high power.
When the secondary battery module is used for motor drive of the vacuum cleaners, motor scooters, or vehicles (electric vehicles or hybrid electric vehicles), a large number of unit batteries are arranged in multiple rows. Accordingly, when assembling the secondary battery module, it is important to arrange the unit batteries to increase the cooling efficiency for unit batteries.
In addition to the cooling efficiency for the unit batteries, when assembling the secondary battery module, it is also important not to increase the size of the secondary battery module.
In details, if the secondary battery module has multiple battery rows (battery row means an aggregate structure in which a plurality of unit batteries are arranged in a row), each battery row is stacked in multiple layers or arranged side by side in a plane. However, the multiple layer structure has a problem in that the overall size of the module is increased as the height of the secondary battery module is increased.
In the meantime, if each battery row is arranged side by side in a plane, the size of the module can be minimized. However, there are problems in that the cooling efficiency for the unit batteries is lowered, and the temperature deviation occurs to cause non-uniform cooling.
This is because, if battery rows are arranged side by side, after passing through the unit batteries in one side battery row, the cooling medium passes through the unit batteries in the other side battery row. This causes the difference of the cooling medium flowed into each battery row.
That is, as the cooling medium passes through one side battery row, the temperature is increased by heat exchange. Then, the other side battery row is cooled by this cooling medium with the increased temperature, and accordingly, there is a big difference between the temperature of the one side battery row and the temperature of the other side battery row.
Therefore, if the battery rows are arranged side by side, as the heat generated from each of the unit batteries in the battery rows is not uniformly discharged, the unit battery's own performance is lowered, and thereby the secondary battery module can not be used for motor drive requiring high power.